Ball joint
This is a continuation of co-pending application Ser. NO. 07/373,907 filed on June 29, 1989 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to a ball joint, especially for steering and transmission rods of motor vehicles. The ball joint includes a bearing shell made of plastic which has a lower shell and an upper shell for the support of a ball head in a joint housing. The lower shell is turned toward a housing opening for a ball stud, and the upper shell is supported against a housing cover through a spring element. The lower shell is joined elastically with the outer rim of the upper shell. 
     2. Background Art 
     From German Disclosure 2,405,160 is known a ball joint of this kind. The ball joint includes a lower shell and an upper shell which are joined and sealed together by a circumferential elastic joining. The elastic joining includes a sealing lip of the upper shell made of elastic material. The sealing lip sealingly engages in a ring groove on the upper rim of the lower shell. For this purpose, the sealing lip is inserted in the ring groove under the pressure of a closing cover. 
     The mounting of this previously known ball joint is expensive because the upper shell and lower shell must be assembled, and are only secured after rolling in the closing cover. Also, the upper shell made of an elastomer material has poor friction, wear and fatigue properties. This may lead to a change of its prestress and the operation characteristics of the ball joint. 
     In German Disclosure 2,913,700 is disclosed a ball joint having a lower shell and an upper shell. The upper shell is supported by a spring against a housing cover. On the upper shell are formed axially directed flanges which engage form-fitting in corresponding openings of the lower shell. However, the form-fitting connection between the lower shell and the upper shell exists only with the ball joint assembled, and must be produced in the mounting. 
     SUMMARY OF THE INVENTION 
     Starting from this, the invention addresses the problem of providing a technically improved ball joint of which the mounting is facilitated, of which the lower and upper shells are secured against a mutual rotation, and of which has better operational properties. 
     For the technical solution of this problem, the invention is characterized by a one-piece bearing shell comprising lower and upper shell portions joined into one part by at least one elastic connection stop. 
     The provision of lower and upper shell portions as a one-piece bearing shell has the advantage that these need not be first assembled and fixed in the installation position in the mounting of the ball joint. At the same time, the form-elastic connection stop make possible a relative axial movement between the lower and upper shells. This makes possible a prestressing of the upper shell and the ball head through the spring element supported against the cover of the housing. Here, the bearing shell material may be chosen with outstanding friction, wear and fatigue properties because the prestressing of the ball head is mainly set through the spring element. With a form-elastic, especially a thin-walled design of the connection stops, relatively inelastic bearing shell materials may also be used. 
     In one embodiment of the invention, connection stops which are displaced and separated by gaps are provided around the vertical axis of the stud through which the form elasticity of the joining of the upper and lower shells is increased. In one advantageous embodiment, three connection stops which are displaced by 120° around the axis of the stud are provided. The three connection stops set back the upper shell even after a tilting in relation to the lower shell. 
     In another embodiment, each connection stop forms between the lower shell and the upper shell, at least one groove extending in the axial direction of the stud. Here, each connection stop is guided in at least a middle section and in the axial direction of the stud so that it can be bent out perpendicularly to the axis of the stud. Also, each connection stop is guided in the side section perpendicular to the axial direction of the stud so that it can be bent out in the axial direction of the stud. In this way, the relative mobility of the upper shell to the lower shell is increased in the axial direction of the stud. Each groove may be limited by one middle section and one side section of the connection stop and the upper shell and the lower shell, respectively. 
     The axial directing of the grooves makes possible also the production of the bearing shells by a relatively simple injection tool, and a better deformability of the bearing shells after injection. The deformability of the bearing shell is still further improved if each groove has a width increasing toward the opening of the groove. 
     In another embodiment, each connection stop has at least one fold so that the connection between the lower and upper shells is designed in the manner of a folded bellows. In this way, the form elasticity of the connection stop is still further increased. Preferably, the folded connection stop forms at least one groove extending in the axial direction of the stud and between the middle section and a side section joining the latter. 
     Finally, in one embodiment of the invention, it is provided that the bearing shell includes a duromer material, especially polyamide (PA) from which excellent friction properties with adequate form elasticity are obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other details and advantages of the subject of the invention are provided from the description which follows, of the respective drawings, in which is shown one preferred form of execution of a ball joint according to the invention. 
     FIG. 1 shows an assembled ball joint of the present invention in longitudinal section; 
     FIG. 2 shows the ball joint of FIG. 1, cut lengthwise and in exploded view; 
     FIG. 3 shows a bearing shell of the ball joint of FIG. 1, in top view; 
     FIG. 4 shows the bearing shell, cut along the line IV--IV of FIG. 3; 
     FIG. 5 shows the bearing shell, cut along the line V--V of FIG. 3; and 
     FIG. 6 shows a connection stop having a fold. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     As shown in FIG. 1, a ball joint has a ball stud 1 of which a ball head 2 is held rotatable and pivotable in a joint housing 4 by a one-piece bearing shell 3. The bearing shell 3 has a lower shell 5 and an upper shell 6 which form together a partially spherical surface supporting the ball head 2 on both sides of the equator. 
     The lower shell 5 is set into a mainly cylindrical housing bore 7 and is axially supported near a housing opening 8 for the ball stud 1 and in a slightly tapered section of the housing bore 7. At the other end, the lower shell 5 is axially supported by a housing cover 9 rolled into the joint housing 4. 
     The upper shell is supported through a conical spiral spring 11 against the housing cover 9. The prestress of the spiral spring 11 determines the pressing pressure of the upper shell on the ball head 2, and determines the operation characteristics of the ball joint. The mobility of the upper shell 6 in relation to the lower shell 5 is assured by three connection stops 12 located between the lower shell 5 and the upper shell 6 and displaced by 120° around the vertical axis of the stud. The connection stops 12 are completely placed in an inset opening 13 of the lower shell 5 for the upper shell 6. 
     As can be seen better from FIG. 2 in the assembly of the ball joint, first the ball stud 1 is set by its ball head 2 into the bearing shell 3. With this, the joint housing 4 by the tapered housing bore 7 exerts a radial force on the lower shell 5 so that the latter near the housing opening 8 presses closely against the ball head 2. Then the conical spiral spring 11 is set onto the upper shell 6 on which it is centered by a centering rim 14. Finally, the housing 9 is set on and fastened in the joint housing 4 by the rolling in of a rolled rim 15. 
     The arrangement and design of the connection stops 12 can be better explained from FIGS. 3 to 5. The connection stops 12 are arranged at three points displaced by 120° around the axis of the stud. Since they are thin-walled and slender, their form elasticity is great. The connection stops 12 extend only into the inset opening 13. They have a middle section 16 running mainly in the axial direction of the stud. This makes possible, in particular, a centering of the upper shell 6 in the lower shell 5. They have also side sections 17, 18 running mainly perpendicular to the axial direction of the stud. This favors a movement of the upper shell 6 in relation to the lower shell 5 in the axial direction of the stud. Referring to FIG. 6, if another middle section 22 adjoins at least one of the side sections 17, 18, the connection stops have a fold 24, and as a folding bellows, have an especially high elasticity of form. 
     Each connection stop 12 defines two grooves 19, 20 extending in the axial direction of the stud. The two grooves 19, 20 are limited by the middle section 16, the side section 17 or the side section 18, and the upper shell 6 or the lower shell 5. The grooves 19, 20 widen toward their groove openings and favor the production of the bearing shell 3 in an injection molding process.